the megalopa and juvenile development of pachygrapsus transversus (gibbes, 1850) (decapoda,...

The Megalopa and Juvenile Development of Pachygrapsus transversus (Gibbes, 1850) (Decapoda,Brachyura) Compared with Other Grapsid CrabsAuthor(s): Augusto A. V. Flores, Maria Lucia Negreiros-Fransozo and Adilson FransozoSource: Crustaceana, Vol. 71, No. 2 (Mar., 1998), pp. 197-222Published by: BRILLStable URL: http://www.jstor.org/stable/20105974 .

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THE MEGALOPA AND JUVENILE DEVELOPMENT OF PACHYGRAPSUS TRANSVERSOS (GIBBES, 1850) (DECAPODA, BRACHYURA) COMPARED

WITH OTHER GRAPSID CRABS

BY

AUGUSTO A. V. FLORES, MARIA LUCIA NEGREIROS-FRANSOZO and ADILSON FRANSOZO

NEBECC (Group of Studies on Crustacean Biology, Ecology and Culture) Departamento de

Zoologia, Instituto de Bioci?ncias and

Centro de Aq?icultura, Universidade Estadual Paulista UNESP, C.P. 510,

18618-000 Botucatu (SP), Brazil

ABSTRACT

Megalopae were reared in the laboratory to the 7th crab stage. The megalopa and 1st crab stage are described and juvenile development was studied with emphasis on pleopodal differentiation.

The megalopal phase, is easily identified, and shares with those of other Grapsinae and Plagusiinae

big size, the presence of many natatory setae, and a series of conspicuous teeth on the inner

margin of the dactyli from the 2nd to 4th walking leg. These features are regarded as adaptive for

settlement in a wave-swept environment, such as the rocky marine intertidal where most of those

species live. Fast development of juvenile pleopods is another characteristic of these subfamilies.

In Pachygrapsus transversus, the sexes can be distinguished from the 2nd crab stage. Gonopod differentiation in males and the basic segmentation of all four pleopod pairs in females are already

concluded at the 5th instar. A review of the available information indicated that settlement of large

megalopae and fast juvenile development, preceding a precocious sexual maturity, are trends in

Grapsinae and Plagusiinae. On the other hand, the Sesarminae pass through a more extensive

juvenile instar sequence and presumably a delayed maturity.

RESUMEN

Individuos en el estadio de megalopa fueron capturados y mantenidos en laboratorio hasta el

7o estadio. La megalopa y el 1er juvenil fueron descritos y el desarrollo juvenil estudiado con

?nfasis en la diferenciaci?n de los ple?podos de estos cangrejos. La fase de megalopa es f?cilmente

reconocida y comparte con otros Grapsinae y los Plagusiinae la gran talla, la presencia de muchas

sedas natatorias y una s?rie de dientes conspicuos en el margen interno de los d?ctilos del 2o al 4o

pere?podo. Estas caracter?sticas se consideran como adaptativas frente a condiciones de exposici?n al oleaje, comunes en el litoral rocoso donde vive la maioria de esas especies. Otra caracter?stica

de esas subfamilias es el r?pido desarrollo de los ple?podos. En Pachygrapsus transversus, los

sexos pueden ser diferenciados desde el 2o estadio juvenil. El desarrollo del gon?podo en machos

y la segmentaci?n b?sica de los cuatro pares de ple?podos en las hembras ya est?n concluidos en

el 5o estadio. Una revisi?n de la escasa informaci?n disponible sugiere que el asentamiento de

? Koninklijke Brill NV, Leiden, 1998 Crustaceana 71 (2)



198 A. A. V. FLORES ET AL.

megalopas de gran talla y el r?pido desarrollo juvenil, antecediendo una maturidad sexual precoz, son una tendencia en Grapsinae y Plagusiinae. Por otro lado, los Sesarminae deben pasar por una

larga secuencia de estadios juveniles y, por lo tanto, alcanzar la maturidad sexual m?s tarde.

INTRODUCTION

Pachygrapsus transversus (Gibbes, 1850) is the common grapsid crab on rocky shores of southern Brazil, but its development is inadequately known. Descrip tions of zoeae are limited to stage I (Lebour, 1944; Ingle, 1987) and stage II

(Cuesta & Rodr?guez, 1994), and only a general illustration is available (Rossig

nol, 1957).

Descriptions of grapsid larvae cover less than 20% of all those known of

Grapsid species (Felder et al., 1985), and these are mainly of Sesarminae and

Varuninae, while the Grapsinae and Plagusiinae remain poorly studied (Wilson,

1980). This biased database is probably related to the fact that plagusiines are

a very restricted group and grapsine larvae are difficult to rear in the labora

tory. Many of the grapsine larval descriptions are limited to the 1st zoea (e.g.,

Paula, 1985; Konishi & Minagawa, 1990), and other rearing efforts failed to

obtain the megalopal stage (Schlotterbeck, 1976; Brossi-Garcia & Rodrigues,

1993). From the scattered complete descriptions of grapsine megalopae, only those of the genus Metopograpsus were obtained by rearing techniques (Kakati,

1982; Pasupathi & Kannupandi, 1986; Fielder & Greenwood, 1983a). Available

megalopal descriptions of the genera Pachygrapsus (Guerao et al., in press) and

Planes (Muraoka, 1973) are based on wild specimens.

Descriptions of early postlarval development in brachyuran crabs are still

scarce, probably due to difficulties in identification (Fransozo & Negreiros

Fransozo, 1987), and in obtaining of juvenile specimens from identified parents

(Hebling et al., 1982). Nevertheless, the existing literature (e.g., Shen, 1935;

Ingle, 1977; Fukuda, 1981; Rieger, 1986) has shown that the acquisition of adult

form, including pleopod sexual differentiation, is highly variable in brachyuran

crabs, including the Grapsidae (Muraoka, 1963; Morita, 1974; Fransozo, 1987;

Hartnoll, 1992; Lee et al., 1994).

In the present paper, the megalopa and the 1st crab instar of P. transversus

are described, and the juvenile development is investigated with emphasis on

the process of pleopod differentiation. The adaptive value of some megalopal features in grapsid crabs are discussed in an ecomorphological approach, and a

preliminary comparative analysis of juvenile development in grapsids is provided.



MEGALOPA AND JUVENILE PACHYGRAPSUS 199

MATERIAL AND METHODS

In April 1995, 17 megalopae were obtained from reefs made by the sabelariid

worm Phragmatopoma lapidosa Kinberg, 1867. Each larva was immediately

placed in an individual 120 ml acrylic vessel, containing pebbles as a hard sub

stratum and partially filled with filtered seawater (34%o S). Every day the water

was changed and the individuals were fed on a combination of live Artemia

nauplii and small pieces of Ulva, shrimp and crab muscle. Temperature was

maintained at 25 ? 1?C and ambient photoperiod. Laboratory rearing was con

tinued until most of the crabs attained the 7th crab stage.

Carapace length, width and instar duration were recorded individually in each

stage. Corpses were fixed in 70% ethyl alcohol. To preserve the exuviae, glycerin was added in a 1 : 1 proportion.

The megalopae and 1st crab instar are fully described. In the following stages,

pleopodal differentiation, carapace morphology and the appearence of genital

openings, are detailed. Drawings were made with the aid of an Olympus binoc

ular microscope and a Zeiss stereomicroscope both provided with a camera lu

cida. Terminology of main setal features are based on Pohle & Telford's (1981)

classification.

RESULTS

Megalopa (figs. 1-5)

Carapace (fig. la, b, c). ?

Length 2.8 mm, width 1.9 mm. Of subtriangular

shape, maximum width at the branchial region nearly twice as long as anterior

width; smooth surface, without protuberances, knobs or grooves; anterolateral

region with lower expansion reaching orbital region (fig. lb); rostrum ventrally curved with a conspicuous median front groove (fig. lc); eyes large, ocular

peduncles well developed (fig. la).

Antennule (fig. 2a). ? Peduncle 3-segmented with 3 plumodenticulate, 4 long

plumose and 0 setae, respectively; endopod unsegmented with 4 terminal simple

setae; exopod 4-segmented with 0, 0, 2, 2 terminal simple setae, and 0, 12, 10, 3

long aesthetascs.

Antenna (fig. 2b). ? Peduncle 3-segmented, with 2, 2, 2 simple setae; flag

ellum 8-segmented with 0, 0, 3, 3, 3 (long), 2, 2 and 2 terminal long, simple setae.

Mandible (fig. 2c). ? Flat with distinct inner margin; 2-segmented palp with

1 and 1 + 10 plumodenticulate setae.




b C

Fig. 1. Pachygrapsus transversus (Gibbes, 1850), megalopa. a, dorsal view; b, carapace; c, ventral

detail of anterior part of carapace; d, abdomen. Scale bars represent 1 mm.

Maxillule (fig. 2d). ? Coxal endite with 9 plumodenticulate setae; basial

endite with 8 smaller and 8 longer, stout plumodenticulate setae and 8 simple

setae; endopod 2-segmented without setae.




Fig. 2. Pachygrapsus transversus (Gibbes, 1850), megalopa. a, antennule; b, antenna; c, mandible;

d, maxillule; e, maxilla. Scale bars represent 0.2 mm.

Maxilla (fig. 2e). ? Coxal endite bilobed, upper lobe with 3 simple and 2

terminal plumodenticulate setae, lower lobe with 10 plumodenticulate marginal, 1 simple marginal, and 6 small plumodenticulate setae; bilobed basial endite,

upper lobe with 12 marginal plumodenticulate setae and lower lobe with 9 plumo




Fig. 3. Pachygrapsus transversus (Gibbes, 1850), megalopa. Maxillipeds. Scale bar represents

0.5 mm.

denticulate setae and 1 long simple seta; endopod unsegmented, without setae;

exopod with approximately 85 small marginal plumose setae.

First maxilliped (fig. 3). ? Coxal endite with 12 marginal + 6 plumodentic

ulate setae; basial endite with 10 marginal + 3 plumodenticulate setae; endopod

unsegmented with 2 subterminal short stout simple setae; well developed epipod




Fig. 4. Pachygrapsus transversas (Gibbes, 1850), megalopa. a, pereopods; b, detail of pereopod

dactyli, 2nd and 3rd above, 4th and 5th below. Scale bars represent 0.5 mm.

with 12-14 marginal, 5-6 long simple setae; 2-segmented exopod with 4, 4 long, terminal plumose setae.

Second maxilliped (fig. 3). ?

Endopod 4-segmented with 1 long, 1, 4, 13

stout simple setae; epipod with 13-16 marginal long simple setae; 2-segmented

exopod with 2 stout simple, 4 long plumose setae.

Third maxilliped (fig. 3). ? Coxa/basis with 6 marginal plumodenticulate

setae and 2 tranverse rows of 9-13 and 4 different sized plumodenticulate setae;

endopod 5-segmented, ischium with 4 small, 12+1 marginal, plumodenticulate

setae; merus with 7 and 3 plumodenticulate setae on inner and outer margins

respectively, carpus with 2 + 4, distal, simple setae; propodus with 11 simple

setae; dactyl with 13 simple and 2 terminal long plumodenticulate setae, epipod well developed with 4 + 2, marginal simple setae, 9 marginal plumodenticulate setae and 25-29 long simple setae; 2-segmented exopod with 4 simple and 4 long terminal plumose setae.




Fig. 5. Pachygrapsus transversus (Gibbes, 1850), megalopa. Pleopods and uropod. Scale bar

represents 0.5 mm.

Pereopods (fig. 4a, b). ? Smooth and slender with a few sparse setae (not

shown) covering first 5 segments, more numerous on dactyli of p2, p3, p4 and

p5; chelipeds similar in shape and size, propodus and dactyl with 3 and 2 smooth

teeth respectively (fig. 4a); propodus from p2 to p4 with ventral terminal spine

projected towards dactyl; dactyl from p2 to p4 ventrally curved with acute ex

tremity and series of 4 sharp teeth, of which 3rd is better developed and followed

in p4 by small additional tooth; p5 dactyl with 3 long feelers (fig. 4b).




Abdomen (fig. Id). ?

Elongated, 6 smooth segments wider than long, first

five ventrally articulated by disto-lateral expansions; 6th somite reduced; telson

with 2 pairs of short subterminal setae and 1 pair of long terminal setae.

Pleopods (fig. 5). ? Well developed; endopods from pl2 to pl5 with 4, 4, 4, 3

little hooked setae and 30-32, 32-35, 28-34, 24-26 large plumose natatory setae;

exopod area decreasing from pl2 to pl5.

Uropods (fig. 5). ?

Endopod absent; exopod with 21 large plumose natatory setae.

First crab (figs. 6-9)

Carapace (fig. 6a). ?

Length 2.3 mm, width 2.8 mm; similar to but narrower

than in the adult; second anterolateral tooth still absent; frontal, orbital and lateral

depressions present; gastric, cardiac and branchial regions already differentiated;

eyes relatively large when compared to adult.

Antennule (fig. 7a). ? Peduncle 3-segmented, proximal segment with 18 and

approximately 25 small plumose setae disposed in transverse and marginal rows

respectively; second and third segment with two and three simple setae; 3-seg mented endopod with 3, 2 and 3 terminal, simple setae; 6-segmented exopod with 0, 1, 1, 4, 4, 3 terminal, simple setae, 8, 7, and 3 long aesthetascs present on 2nd, 3rd and 4th segments, respectively.

Antenna (fig. 7b). ? Peduncle 3-segmented, with 7 small, 3 large and 0 plumo

se setae and 0, 3, 3 simple setae; flagellum 8-segmented with 3, 2, 4, 3, 4, 1, 1

and 3 simple setae.

Mandible (fig. 7c). ? With 1 median tooth on differentiated inner margin;

3-segmented palp with 1, 7 small plumose setae and 3 small plumose + 14-16

small plumodenticulate setae.

Maxillule (fig. 7d). ? Coxal endite with 8 + 14 simple, 7 marginal plumose

and 5 terminal stout plumodenticulate setae; basial endite with 1 long plumose, 5 marginal long plumodenticulate and 23 subterminal + 6 stout simple setae;

endopod 2-segmented with 5 long and 4 small plumose + 2 simple setae.

Maxilla (fig. 7e). ? Bilobed coxal endite, upper lobe with 9 marginal plumose

setae, lower lobe with 7, 5 + 10-13 marginal, plumose setae; bilobed basial endite,

upper lobe with 4 small and 14-16 marginal different sized, plumose setae, lower

lobe with 4 small and 5+2 longer marginal plumose setae; endopod unsegmented and smooth; exopod with approximately 120 small marginal plumose setae.

Sternum (fig. 6b). ? First 3 segments fused, other 5 clearly defined; pair of

buttons on the 5th sternite; 8th sternite with slight longitudinal depression; genital

openings still absent.




Fig. 6. Pachygrapsus transversus (Gibbes, 1850), first crab, a, dorsal view; b, sternum; c, abdo

men. Scale bars represent 1 mm.

First maxilliped (fig. 8). ? Coxal and basial endites with borders almost

completely covered with plumose setae; endopod 2-segmented, proximal segment with inner margin covered with small plumose setae; distal segment divided

in two subsquare surfaces, each with 10 simple setae on distal margin, well

developed epipod with 18-23 and approximately 50 marginal, long simple setae;

2-segmented exopod with 1 small + 4 longer and 6 terminal long, plumose setae.

Second maxilliped (fig. 8). ?

Endopod 6-segmented. 1st and 2nd segment with 4 and 2 marginal plumose setae; 3rd segment with 4 long stout simple setae and inner margin covered with different sized plumose setae; 4th segment




Fig. 7. Pachygrapsus transversus (Gibbes, 1850), first crab, a, antennule; b, antenna; c, mandible;

d, maxillule; e, maxilla. Scale bars represent 0.2 mm.




Fig. 8. Pachygrapsus transversus (Gibbes, 1850), first crab. Maxillipeds. Scale bar represents

0.5 mm.

with 4 small simple setae, 5th segment with 7-9 plumose setae on the upper

margin and a row of 7 very small distal plumose setae; 6th segment completely bordered with plumose setae; epipod with 25 marginal long simple setae; exopod

2-segmented, inner margin of 1st segment with 8 plumose setae and 8-11 small

simple setae among them, outer margin with 11 plumose setae of decreasing size

from proximal to distal, 2nd segment with 3 simple setae on upper margin and

terminal 6 long plumose setae.




Fig. 9. Pachygrapsus transversus (Gibbes, 1850), first crab. Pereopods. Scale bar represents

0.5 mm.

Third maxilliped (fig. 8). ? Surface and upper margin of coxa/basis cov

ered with different sized plumose setae; endopod 5-segmented, 3 plumose setae

on lower margin of ischium and several covering inner margin, carpus with

5 + 6 plumodenticulate and 8 marginal plumose setae; merus with 11-13 dis

tal plumodenticulate setae; propodus and dactylus bordered and covered with

several plumodenticulate setae, dactylus with 2 distinct long plumodenticulate

setae; epipod well developed, proximal portion covered and bordered with sev

eral plumose setae, distal portion margined with 50-55 long simple setae; exopod




2-segmented, proximal segment with 8, 8 small and 1 distal, marginal plumose

setae, distal segment with 3 subterminal and 6 long terminal, plumose setae.

Pereopods (fig. 9). ?

Chelipeds similar to those of adult, but without defined

dentition; walking legs with distribution pattern of setae (not shown) resembling the adult form, grooves in meri already present.

Abdomen (fig. 6c). ? Lateral margins of somites still rounded; 2nd to 5th

somite with characteristic transverse striae which disappear in later instars.

Pleopods. ? Absent. First stage crabs with vestigial, shrivelled pleopods were

captured occasionally in the wild.

Second crab (figs. 10a, e, 11)

Males and females can be already distinguished at this instar. First pair of

pleopods in males from small biramous appendages to longer distally grooved

gonopods (fig. 10a). Male genital openings in lateral ends of sternite 8 (fig. 11).

In females, 2nd to 5th pleopod pairs present. All pairs biramous, with endopod

equal to or longer than exopod (fig. 10e). Female genital openings present on

6th sternite (fig. 11).

Carapace wider (table I), second anterolateral tooth (missing in the previous

stage) present. At this stage the crabs are almost miniature adults.

Further juvenile stages (fig. lOb-d, f-h)

Differentiation of pleopods continues until the 5th crab stage in both males

and females.

Males. ? 3rd instar: pli with distal groove and longitudinal sulcus; pl2 already

present (fig. 10b). 4th instar: pli greatly enlarged and closely resembling that of

adult, terminal region laterally curved, distal groove larger, few setae on upper

Table I Juvenile development of Pachygrapsus transversus (Gibbes, 1850). Carapace

length, carapace length/width ratio and duration of each juvenile stage in labora

tory conditions. Variation expressed as standard deviation, numbers in brackets

indicate number of observed crabs

Juvenile instars

_ JI JH JIII JIV JV JVI JVII

Length (mm) 2.3+0.1 2.6+0.2 3.0+0.2 3.5+0.3 4.1+0.5 4.6+0.5 5.0+0.4

(9) (14) (15) (16) (15) (13) (7) LAV 0.83 0.75 0.72 0.71 0.73 0.72 0.74 Duration (days) 17.9+8.0 17.8+6.2 18.6+4.7 22.5+5.1 20.5+7.5 25.8+4.9 28

(17) (17) (17) (17) (11) (8) (1)




Ml} \\ i i I-1

Fig. 10. Pachygrapsus transversus (Gibbes, 1850), pleopods from the 2 to 5 crab stage; a-d, males; e-h, females, from left to right pl2 to pl5. Scale bars represent 0.5 mm.

external margin; pl2 closer to pll (fig. 10c). 5th instar: gonopods even more

disproportionate, linked by thick calcified bridge, number of setae increased; pl2 with small distal groove (fig. lOd).

Females. ? 3rd instar: in all 4 pleopods 2-segmented endopod always larger

than exopod (fig. lOf). 4th instar: all pleopods much enlarged, with exopod



212 A. A. V FLORES ET AL.

Fig. 11. Pachygrapsus transversus (Gibbes, 1850), sternum of males and females in the 2nd crab

stage. Scale bar represents 1 mm.

Fig. 12. Pachygrapsus transversus (Gibbes, 1850), abdomina of males (above) and females (below)

from the 2nd to 7th crab stage. Scale bar represents 1 mm.




differentiated from protopod and some sparse setae present, pl4 with 3-segmented

endopod and 2-segmented exopod (fig. 10g). 5th instar: pleopods more setose

and segmented; all endopods 2-segmented; exopods 6, 6, 6 and 5-segmented;

segments with distally concentrated setae; pll longer than rest, with longer setae

(fig. 10h). Females in 4th and 5th instars showed some variability in pleopod segmentation

and setation. One 4th instar female presented a typical 5th instar segmentation, and a 5th instar female with expected setation had segmentation, as in a typical 4th instar.

Abdominal sexual dimorphism can only be clearly observed after the 6th stage.

At the 7th instar, the abdomen of females resembles the pre-puberal shape found

in wild living specimens, while males present a typical adult form (fig. 12).

At the 3rd instar, the carapace shape becomes virtually the same as in the adult,

with a similar length/width ratio. Time elapsed between moults increased with

size, as expected (table I). However, intermoult period and instar size recorded

may vary from the wild.

DISCUSSION

Rossignol (1957) published a dorsal view of a P. transversus megalopa from

Central Western Africa. Measurements and general morphological characteristics

are compatible with the present descriptions, but the carapace ornamentation

shown was not observed in the current study. This difference may correspond to local coloration patterns, as in adult crabs, or it may be a result of genetic

divergence, evidenced by Cuesta & Schubart (in prep.), between populations on

both sides of the Atlantic.

The megalopa of P. transversus can be readily distinguished from other Pachy

grapsus species. A full description of the megalopa of P. crassipes Randall,

1840 is not available, but Hiatt (1948) provided valuable information regard

ing its general morphology. Among other records, the author found a mean

carapace length of 5.6 mm, a much higher size than the 2.8 mm recorded for

P. transversus. Considering that both measurements were obtained from wild

specimens, this difference is sufficient to distinguish these species. The mega

lopa of P. marmoratus (Fabricius, 1787), described by Guerao et al. (in press) can also be easily distinguished from the megalopa of P. transversus, since the

former presents a higher number of teeth (7) on the inner margin of the dactyli

from p2 to p5, and 5 setae in the maxillule endopod, which are absent in the

latter. The morphological similarity between the megalopa of P. transversus

and Planes cyaneus Dana, 1851, described by Muraoka (1973), is equivalent




to that found within the genus Pachygrapsus. Otherwise, those 2 genera differ

remarkably from the megalopal descriptions by Kakati (1982) and Pasupathi &

Kannupandi (1986) of mangrove grapsines of the genus Metopograpsus. The megalopal stage in most brachyuran crabs is considered an obligatory

link between the zoeal planktonic phase and the adult benthonic crabs (Rice,

1981). Therefore, this last larval phase must be able to efficiently locate and

then settle in a favourable environment. In order to accomplish these tasks

some specializations regarding chemical perception, locomotion and substrate

adherence, are expected to have evolved in these larvae. Some morphological characteristics of grapsid megalopae from formal larval descriptions, were chosen

to assess the power of swimming and substrate grasping. For this purpose, it

was assumed that: first, larger megalopae are more likely capable to challenge

eventually weak water movements; second, number of natatory setae in pleopods are proportional to swimming stroke; and third, inner serratiform margin of

pereopod dactyli are useful to avoid wave dislodging. In table II, these features are presented in a subfamilial order, in which species

belonging to the same genus are grouped together when no relevant differences

were recorded among them. An additional column of species/genus habitat is

also provided.

Perhaps the most obvious trend from this analysis is the morphological di

chotomy between the Sesarminae and a group enclosing the Plagusiinae and

the Grapsinae. Most Sesarmine megalopae settle in relatively sheltered envi

ronments, such as mangroves and other estuaries. With a few exceptions, these

settlers are small and do not possess a high number of natatory setae nor spe

cialized grasping dactyli. On the other hand, plagusiine and grapsine megalopae, are larger and are provided with more natatory setae and armed dactyli. This

trend was quite expected, since this second grouping is almost totally composed

by inhabitants of wave exposed environments.

The grasping structures of dactyli comprise both spines; i.e., stout large out

grows, and teeth; i.e., acute expansions of the segment itself. These projections

may play an equivalent role, but they are certainly not homologous. Among the Brachyura, prominent spines are also present on the dactyli of some majids

(e.g., Kurata, 1969; Christiansen, 1973; Negreiros-Fransozo & Fransozo, 1991;

Hiyodo & Fransozo, 1994), but a series of noticeable teeth is only present in

some grapsids. All the Grapsinae and the Plagusiinae present well developed teeth on the inner margin of dactyli from p2 to p4. This can be an apomor

phic condition distinguishing this group. Small teeth, a second condition that

might have evolved independently, are present in some Varuninae, namely Hemi

grapsus sanguineus (De Haan, 1835); H. nudus (Dana, 1851) and Brachynotus




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atlanticus Forest, 1957. Grapsid species with spines include riverine forms, in

which megalopae migrate from the sea back to the adult habitat, and marine

species, as is the case of Cyclograpsus integer H. Milne Edwards, 1837, the

single sesarmine presenting this feature. It is interesting to observe that there is

no described estuarine species with armed dactyli.

Plagusiines can be easily differentiated from grapsines, since the toothed dactyl condition extends to the 5th pereopod. Furthermore, in the Grapsinae the maxil

lule endopod is poorly setose, and in the case of Metopograpsus frontalis Miers,

1880, M. latifrons (White, 1847) and P. transversus, setae are absent.

This analysis does not intend to clearly separate each grapsid subfamily, but

attempts link the importance of some characteristics of the megalopal stage to

systematics; a suggestion that was previously raised by Rice (1981). Unfortu

nately, the available information concerning grapsid megalopal morphology is

not enough to allow a consistent phylogenetic analysis of the group at present. One of the most remarkable characteristics of the grapsine and, especially,

plagusiine megalopae is their size. The attainment of a big size at settlement,

besides its adaptive value mentioned above, may also allow the shortening of the

juvenile phase. Furthermore, Hines (unpubl. data) pointed out that larger recruits

may pass through fewer moults to attain the size at sexual maturity, which is an

alternative life history/growth adaptation to minimize this risky process.

The first crab stage in P. transversus is already very similar to the adults. The

density and distribution pattern of setae on the cephalic appendages and maxil

lipeds are typical of more advanced crab stages, such as those studied by Morita

(1974) in Eriocheir japonicus (De Haan, 1835). Furthermore, some behavioural

patterns like running, hiding under stones and feeding, clearly resemble the adult

life style. Sexes can be distinguished at the 2nd crab stage, and in subsequent instars the pleopods of both undergo profound and rapid differentiation. Captive

juvenile crabs from the 5th to 7th stage roughly correspond to the 6-7 mm carapace

length in wild individuals, which are usually about to achieve the puberty moult

(Flores & Negreiros-Fransozo, in prep.). Hence, it can be considered that this

species undergoes abbreviated juvenile development. In a similar way, the sexes

in the congener P. marmoratus can be distinguished in the 2nd or 3rd crab stage

and very small ovigerous females can be observed in the wild (Vernet-Cornubert,

1958). In the Plagusiinae, sexes can often be distinguished even earlier, and some

records on early postlarval stages revealed a surprisingly brief juvenile develop ment occurring in this group. Initial male gonopod differentiation at the 1st instar

was recorded by Hartnoll (1992) in Percnon abbreviatum (Dana, 1851) and by Muraoka (1963, 1965) in Plagusia dentipes (De Haan, 1835) and P. depressa




(Fabricius, 1775) respectively. Based on the 1st crab and smaller adult crab sizes, Hartnoll (1992) also estimated that sexual maturity in Percnon abbreviatum and

P. guinotae (Crosnier, 1965) is attained in the 3rd and 4th stages respectively. Genital openings in the Varunine genus Eriocheir are visible at the 1st crab

stage (Hoestlandt, 1948; Lee et al., 1994), but in E. japonicus shrivelled non

functional pleopods remain until the 3rd instar and sexual pleopod differentiation

begins only at the 4th stage (Morita, 1974). In the Sesarmine species Sesarma

rectum Randall, 1840, remaining pleopods are present in the 1st and 2nd instars; at the 3rd stage, these structures disappear, and only at the 12th stage the defini

tive pleopods can be observed and the young crabs sexed (Fransozo, 1987). This extremely gradual process of pleopod differentiation throughout juvenile

development is likely to persist in other Sesarminae, as seems to be the case in

Armases rubripes (Rathbun, 1897). In this species, pleopod differentiation does

not take place at least until the 6th stage (Vieira & Rieger, pers. comm.).

The present comparative analysis shows that settlement and early postlarval

development in grapsid crabs tend to fall into two major patterns. Species that

recruit as larger benthic forms, mainly represented by the Grapsinae and the

Plagusiinae, present a shorter juvenile development and, therefore, a precocious sexual maturity. On the other hand, smaller recruits and long juvenile develop

ment, preceding delayed sexual maturity, seem to be characteristics of an alter

native strategy adopted chiefly by sesarmines. However, more work devoted to

the development of juvenile crabs is required before outlining more precise and

conclusive trends.

ACKNOWLEDGEMENTS

The authors are grateful to anonymous reviewers for providing valuable com

ments on earlier drafts of this manuscript. The present contribution was supported

by the "Funda?ao de Amparo ? Pesquisa do Estado de S?o Paulo" ? FAPESP

(proc. # 94/01688-3) as a Master Science fellowship to the first author.

Appendix I. Species and respective sources used in table II

SESARMINAE: Aratus pisonii: Warner (1968); Bresedium breviceps: Fielder & Greenwood

(1983b); Chasmagnathus convexus: Baba & Fukuda (1972); C. granulata: Boschi et al. (1967);

Cyclograpsus cinereus: Costlow & Fagetti (1967); C. integer. Gore & Scotto (1982); C. puncta

tus: Fagetti & Campodonico (1971); H?lice crassa: Wear & Fielder (1985); H. tridens tridens and H. t. wuana: Baba & Moryiama (1972); Helograpsus haswellianus: Fielder & Greenwood (1984);

Armases rubripes: Diaz & Ewald (1968); Sesarma catenata: Pereyra Lago (1987); S. {Holome

topus) dehaani: Baba & Myiata (1971); S. guttatum: Pereyra Lago (1993); S. meinerti: Pereyra

Lago (1989); S. rectum: Fransozo & Hebling (1986); S. reticulatum: Costlow & Bookhout, (1962); S. ricordi: Diaz & Ewald (1968).




Varuninae: Brachynotus atlanticus: Rodriguez et al. (1992); Cyrtograpsus altimanus: Scelzo

& Lichtschein de Bastida (1978); Eriocheir jap?nica {= E. japonicus): Morita (1974); E. rectus:

Shy & Yu (1992); Gaetice depressus: Muraoka (1971); Hemigrapsus nudus and H. oregonensis: Hart (1935); H. sanguineus: Muraoka (1971); Varuna litterata: Ryan & Choy (1990).

PLAGUSIINAE: Percnon abbreviatum: Hartnoll (1992); P. gibbesi: Paula & Hartnoll (1989);

P. guinotae and P. planissimum: Hartnoll (1992); Plagusia chabrus: Wear & Fielder (1985);

P. dentipes: Muraoka (1963); P. depressa: Muraoka (1965).

GRAPSINAE: Metopograpsus frontalis: Fielder & Greenwood (1983a); M. latifrons: Kakati

(1982); M. latifrons (as M. maculatus): Pasupathi & Kannupandi (1986); Pachygrapsus crassipes: Hiatt (1948); P. marmoratus: Vernet-Cornubert (1958) and Guerao et al. (in press); Planes cyaneus:

Muraoka (1973) and Wear & Fielder (1985); P. minutus: Lebour (1944).

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Received for publication 10 December 1996.



the megalopa and juvenile development of pachygrapsus transversus (gibbes, 1850) (decapoda,...

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